| Soybean peptide is the hydrolysate of soy protein and a mix of low peptides which composes of three to six residences. Its molecular weight is below 1000Da. They were also defined as soybean bioactivity peptide or soybean functional peptide due to their good process function and bioactivity beneficial to human body, for example, it has the resistant to tiredness and oxidation,lowered cholesterol and blood pressure and so on. Soybean peptide has been widely used in food, medicine and cosmetic fields, and focused by researchers for their potential of functional food. At present, the research of soybean peptide is booming. However, there is much less research on the correlation between degree of hydrolysis, protease enzyme system distribution and molecular weight distribution, which has not been reported so far.In this research, the optimal fermentation conditions for the production of soybean peptide by solid-state fermentation was discussed, which using soybean meal as raw material; Aspergillus oryzaeA-9005, Aspergillus niger3.350 and double strain as fermentation strain. This paper focused on the following four aspects: First, determination of the molecular weight distribution of soybean peptide. Second, make sure the correlation between degree of hydrolysis and molecular weight distribution. Third, make sure the correlation between protease enzyme system distribution and molecular weight distribution. Fourth, optimize the conditions of fermentation of soybean peptide. The main results were described as following:1. Aspergillus niger3.350(1)Molecular weight distribution: mainly distributing in MW>1355Da; the ratto of low-molecular-weight peptide was low; the ratto of oligopeptide was moderate, when fermentation time was at 84h, the maximum ratto was 47.32%.(2)Degree of hydrolysis: rise at all times.(3)Protease activity: 0-60h-living increase gradually, 72h after live-started to decline.(4)Peptide conversion rate: rise at all times, the maximum was 68%.(5)Oligopeptide conversion rate: when fermented at 84h,the maximum was 28.39%.2. Aspergillus oryzaeA-9005(1)Molecular weight distribution: mainly distributing in MW>1355Da; the ratto of low-molecular-weight peptide was slightly low; the ratto of oligopeptide was moderate, when fermentation time was at 72h, the maximum ratto was 31.21%.(2)Degree of hydrolysis: rise all the while.(3)Protease activity: 0-60h-living increase gradually, 72h after live-started to decline.(4) Peptide conversion rate: rise all the while, the maximum was 48%.(5)Oligopeptide conversion rate: when fermented at 96h,the maximum was 12.24%.3. The mixture bacteria of Aspergillus niger3.350 and Aspergillus oryzaeA-9005(1)Molecular weight distribution: mainly distributing in MW>1355Da; the ratto of low-molecular-weight peptide was much low; the ratto of oligopeptide was higher than single strain above, the average of which was more than 50%. When fermentation time at 132h, the maximum ratto was 69.90%.(2)Degree of hydrolysis: rise all along.(3)Protease activity: first increased then decreased, when fermentation time was at 132h, the maximum of protease activity was 1219U/g.(4)Peptide conversion rate: rise all along, the maximum is 75.54%.(5)Oligopeptide conversion rate: when fermented at 132h,the maximum was 49.29%.4. Under the condition of not much more obvious correlation between degree of hydrolysis, protease enzyme system distribution and molecular weight distribution, higher conversion rate of soybean peptide and reasonable molecular weight distribution was determined as the optimal fermentation conditions. The results showed the best fermentation parameter combinations were the mixture of Aspergillus niger3.350 and Aspergillus oryzaeA-9005, natural pH, the content of soybean meal was 91%, inoculation amount 10%, the ratio of inoculation was 2∶1, the fermentation temperature was at 30℃, the fermentation time was at 132h. Under this condition, the ratto of functional soybean peptide was 70% and oligopeptide conversion rate was 49%.
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